ProPhoto RGB color space

CIE 1931 xy chromaticity diagram showing the chromaticities enclosed by the ProPhoto RGB color space and location of the primaries. The D50 white point is shown in the center. The areas of the triangle that are outside the colored area are imaginary colors.

The ProPhoto RGB color space, also known as ROMM RGB (Reference Output Medium Metric), is an output referred RGB color space developed by Kodak. It offers an especially large gamut designed for use with photographic output in mind. The ProPhoto RGB color space encompasses over 90% of possible surface colors in the CIEL*a*b* color space, and 100% of likely occurring real world surface colors documented by Pointer in 1980,[1][2] making ProPhoto even larger than the Wide Gamut RGB color space. The ProPhoto RGB primaries were also chosen in order to minimize hue rotations associated with non-linear tone scale operations. One of the downsides to this color space is that approximately 13% of the representable colors are imaginary colors that do not exist and are not visible colors.

When working in color spaces with such a large gamut, it is recommended to work in 16-bit color depth to avoid posterization effects. This will occur more frequently in 8-bit modes as the gradient steps are much larger.

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The development of ProPhoto RGB and other color spaces is documented in an article[3] summarizing a presentation by one of its developers Dr. Geoff Wolfe at Kodak, now Senior Research Manager at Canon Information Systems Research Australia, at the SPIE Color Imaging Conference in 2011.